The IV fluids you were given while in the hospital are notorious for causing temporary water retention. Water retention can also be as a result of the trauma to the body from the surgery itself. But if you have any concerns that it may be a more serious condition or if doesn't subside, call your doctor right away!

I had surgery a month ago today on my stomach. Im still swollen and feel hard around my stomach. I have been told it can last up to 6 weeks probably even 2 months!

Messes with my anorexic head but I guess I should listen to the advice the doctors give! Anyway, I know that isnt your question but in answer it seems that you do get swelling and water retention after surgery!!